Just in case you were needing a thermal printer test image …

Here you go, then. It should print perfectly on an 58 mm thermal printer. It features:

• 12½% grey scales (clockwise, from right) — ordered, Hilbert (clump=5), Floyd-Steinberg, and halftone (4 pixel/cell).
• Vertical and horizontal test lines.
• Classy woven background.
• Roughly 50% grey overall, so shouldn’t cause your printer too much grief.
• Entirely free of licence restrictions.

very simple python image printer: scruss/esc-pos-image.py